The transmission of variant Creutzfeldt-Jakob disease (vCJD) to humans from bovine-spongiform encephalopathy (BSE)-contaminated meat, and the transmission of BSE by intra-venous inoculation of peripheral blood to experimental animals raises two important questions: 1) how are prions from food transported across the intestinal epithelial barrier, and 2) how do prions in the peripheral blood cross the endothelial blood brain barrier (BBB). These questions have gained increasing importance with the realization that close to one million BSE infected cows may have entered the human food chain. An emerging concern is the spread of Chronic Wasting Disease (CWD), a prion disease of the deer and elk in certain parts of USA, and the uncertainties regarding its transmission to livestock and humans. Despite these concerns, surprisingly little is known about the mechanism(s) by which the infectious prion or PrP-scrapie (PrPsc), a protein of 27-30kDa, is transported from the intestine or peripheral blood to the central nervous system. Preliminary data from my laboratory demonstrate that PrPsc in sporadic CJD (sCJD) brain homogenates is transported across epithelial cells in association with ferritin. When considered in context with additional data indicating an upregulation of brain ferritin levels in response to redox active iron in the brain parenchyma of sCJD cases, this observation raises important questions. We hypothesize that the transport of PrPsc across epithelial and endothelial cell barriers is facilitated by proteins like ferritin that have a defined transcytotic route, and that imbalance of brain iron homeostasis contributes directly to the pathogenesis of certain prion disorders, and indirectly by promoting infectivity through ferritin. Thus, the central goal of this proposal is to investigate the role of PrPs-associated proteins including ferritin and transferrin in facilitating its transport across the intestinal epithelium and the BBB, and to evaluate the role of redox active iron in the pathogenesis of prion disorders. The proposed studies will be carried out in three specific aims. In aim 1, the role of ferritin, transferrin, and other PrPsc-associated proteins in the transport of PrPsc across in vitro models of human intestinal epithelial cell barrier and the BBB will be evaluated. In aim 2, the results obtained from in vitro models in aim 1 will be confirmed in vivo in transgenic mice expressing human PrP. In aim 3, the role of redox active iron in the pathogenesis of priori disorders will be investigated using ferritin over-expressing and H-ferritin deletion transgenic mice. These studies will help in evaluating the risk of human population to BSE, vCJD, and CWD infection, and help in understanding the mechanism of prion disease pathogenesis.